The invention concerns an electronically commutated motor having a permanent-magnet rotor and a stator.
Electronically commutated motors of this kind are known in many variants.
One object of the invention is to make available a new electronically commutated motor.
According to the invention, this object is achieved by an electronically commutated motor having a rotor and a stator; having a stator winding arrangement which can be supplied via a full bridge circuit with current from a direct-current source, which full bridge circuit has in each bridge arm an upper MOSFET (Metal oxide Semiconductor Field Effect Transistor) transistor that is connected to a positive line of the direct-current source and a lower transistor that is connected to a negative line of the direct-current source; having a commutation arrangement for commutating said transistors, which commutation arrangement is configured in order, as a function at least of the position of the rotor, in a first bridge arm to switch on only one transistor and in a second bridge arm, controlled by a PWM signal, alternatingly to switch on the upper and the lower transistor, and having an arrangement which, as a function of at least one motor variable, upon the occurrence of a braking current in the bridge circuit that exceeds a predefined value, modifies the pulse duty factor of said PWM signal in such a way that the current produced by the motor in generator mode is reduced.
An electronically commutated motor of this kind is highly suitable for drive applications in which external influences can cause a desired rotation speed to be exceeded, as a result of which the motor, with this type of bridge circuit, automatically transitions into braking mode; and it is guaranteed that motor limit values defined in the context of said braking mode are not, or cannot substantially be, exceeded.
Another solution to the stated object is achieved by an electronically commutated motor having a rotor and a stator; having a stator winding arrangement which is supplied via a full bridge circuit with current from a direct-current source, which full bridge circuit has in each bridge arm an upper NMOS transistor that is connected to a positive line of the direct-current source and a lower transistor that is connected to a negative line of the direct-current source, and there is associated with each upper transistor of a bridge arm a storage capacitor that can be charged via the lower transistor of said bridge arm and serves to supply said upper transistor with a control voltage; having a commutation arrangement for commutating said transistors, which commutation arrangement is configured in order, as a function at least of the position of the rotor, in a first bridge arm to switch on only one transistor and in a second bridge arm alternatingly to switch on the upper and the lower transistor, the motor rotation speed being monitored and, in the event it falls below a predefined rotation speed value, after a predefined time has elapsed the upper transistors of the full bridge circuit being briefly blocked and the lower transistors of the full bridge circuit being briefly switched on, in order to charge the storage capacitors of the upper transistors and thereby to ensure reliable control of said upper transistors even at low motor rotation speeds or when the motor is at rest.
The result is that in the context of a motor having a full bridge circuit of this kind with NMOS transistors, operability is ensured even if the rotation speed becomes very low or even decreases to zero.
The stated object is also achieved by a method for operating an electronically commutated motor having a permanent-magnet rotor and a stator; having a stator winding arrangement which can be supplied via a full bridge circuit with current from a direct-current source, which complete bridge circuit has a plurality of bridge arms and has in each bridge arm an upper MOSFET transistor that is connected to a positive line of the direct-current source and a lower transistor that is connected to a negative line of the direct-current source; having a commutation arrangement for commutating said transistors, which commutation arrangement is configured in order, as a function at least of the position of the rotor, in a first bridge arm to switch on only one transistor and in a second bridge arm, controlled by a PWM signal, alternatingly to switch on the upper and the lower transistor; and having a microprocessor or microcontroller, hereinafter called a microprocessor, comprising the following steps: in the microprocessor, based on a synthetic model of the motor, monitoring occurs as to whether the direct-current voltage conveyed to the motor is at a predefined relationship to the voltage induced in the motor; if the relationship is not being adhered to, correspondingly modifying, by the microprocessor, the pulse duty factor of the PWM signal with which the upper and the lower transistor of the second bridge arm are alternatingly switched in order to correct said relationship, in order by means of said change in the pulse duty factor to counteract any excursion beyond the predefined relationship.
The result that can thereby be achieved, by correspondingly configuring the software, i.e. by means of a synthetic (and optionally simplified) model of the motor, is that the latter operates in a range in which it is not at risk of overload. In some motor types with a high specific output, for example, too high an operating current or braking current could generate such a high stator magnetic field that the permanent-magnetic rotor becomes demagnetized; this can be prevented in very simple fashion by the method according to the present invention, significantly enhancing operating reliability.
The stated object is achieved in a different fashion by means of an electronically commutated motor having a rotor, and having a stator on which is arranged a stator winding arrangement with which is associated a full bridge circuit having a plurality of parallel bridge arms, each of which has an upper transistor that is connected to a positive line of a direct-current source and a lower transistor that is connected to a negative line of the direct-current source, the two transistors of a bridge arm each having associated therewith a control circuit which as a function of a first input signal can be activated and deactivated and in the deactivated state blocks both transistors of the associated bridge arm, and which as a function of a second input signal, in the state activated by the first input signal, can be switched over in such a way that either the upper transistor or the lower transistor is made conductive; furthermore having a microprocessor or microcontroller, hereinafter called a microprocessor, for generating the first input signal at a first output and for generating the second input signal at a second output; and having a third input signal in the form of a PWM signal with a controllable pulse duty factor, which third input signal can be conveyed to the control circuit from a PWM signal source in parallel with the second input signal and is effective only if the second output of the microprocessor is switched over into a predefined switching state.
It is thereby possible for the PWM signal to be fed in only just before the control circuit, thus greatly simplifying the circuit; the microprocessor nevertheless retains complete control over the control circuit, so that (independently of the PWM signal) it can control the upper and lower transistors of the associated bridge arm (for example when used as a charge pump), but on the other hand, after the second output of the microprocessor has switched over into the predefined switching state, allows said bridge arm to be controlled by the PWM signal, for example to control a motor parameter.